The present invention relates to a process for producing silicone resins, the silicone resins themselves and, more particularly, the present invention relates to silicone resins useful in forming high quality mica laminates.
In producing silicone resin-mica laminates a solvent solution is formed with the silicone resin in which the solids content of the silicone resin may vary anywhere from 20% by weight to 75% by weight. Silicone resins that have been used for this purpose in the past are, for instance, such as those described in the patent application 8SI-1212, Ser. No. 115,715 by Duane F. Merrill, entitled Fast-Curing Silanol-Containing Organopolysiloxane Resins and a Method for Making Them and now abandoned. The procedure for making the laminates when the solids content of the solution is between 20% to 50% by weight, is to take the mica paper and immerse it in the solution. In such immersion technique the mica paper must have a 12% by weight solids pickup of the silicone resin on the mica paper.
In another procedure, when the solids content of the silicone resin solvent solution is between 50 to 75% by weight then the silicone resin solvent solution is applied to both sides of the mica paper by trickling it on the mica paper or brushing it on the mica paper. In any case, for a proper mica laminate and whichever method is applied, there must be 8 to 12% by weight of silicone resin pickup by the mica paper. The silicone resin coated mica paper is then taken and air dried for a short period of time. Then various numbers of the coated paper are put under two pressure plates (the number of mica papers being inserted being put together depends on the thickness of the mica laminate that is desired) and then the layers of mica paper between the pressure plates are heated to temperatures of 100.degree. to 150.degree. C. under pressure varying anywhere from 100 psig to 4,000 psig for 30 minutes or more of pressing time. At the end of this period, the press is cooled and the laminate is taken out of the pressure plates and inspected for density, delamination and for blistering. If the laminate has the proper density it has a metallic sound when struck against a hard object. Then the laminate is post baked by putting it under pressure plates again and heating it in an oven at a temperature range from 100.degree. C. up to 300.degree. C., as the post baking progresses for a period of anywhere from 8 hours to 30 hours. Upon completion of this post baking, the silicone resin mica laminate is taken out and is ready to be used.
With prior art silicone resins it was found that in some cases when the laminate was press-cured initially that the laminate blistered and after the press-cure would not have the proper pressed density. In the past, it was also found that in the post bake cycle, the laminate would not retain its press density and that in some cases the silicone resin would soften and thus produce a poor laminate. It was especially noticed that delamination occurred when the final laminate was punched or cut as is usual in fabricating articles from such laminates. In some cases such delamination and loss of press density was avoided by using the pressure plate during the post bake cycle. In another case, even this procedure was not helpful in preventing delamination or loss of press density of the final laminate during the post bake cycle.
Another problem with the production of such silicone resin mica laminates was the use of the catalyst in the silicone resin solids solution. Usually such a catalyst was a metal salt of a carboxylic acid. It was found that such catalyst, in some cases, would cause the silicone resin to cure too quickly and in some cases would not cause the silicone resin to cure with sufficient rapidity. Accordingly, there is a need in the mica laminate art for silicone resins which, when a mica laminate is formed from it, will retain 90% of its pressed density during the post cure cycle, will not blister during the post cure cycle even in the absence of pressure plates and in which the final laminate will not delaminate or come apart upon the mica laminate being cut or punched.
Accordingly, it is one object of the present invention to provide a process which is economical and efficient for producing a silicone resin useful for forming mica laminates.
It is an additional object of the present invention to provide a process for producing a silicone resin which can be utilized to make mica laminates such that the mica laminates will not delaminate and have the proper pressed density upon the mica laminate being punched or handled in various ways to fabricate articles therefrom.
It is yet another object of the present invention to provide a silicone resin and catalyst which is useful in forming a mica laminate, which mica laminate does not have to be put under pressure plates during the post bake cycle where the mica laminate will retain 90% of its pressed density and will not blister or delaminate upon use.
It is still another object of the present invention to provide a process for making a silicone resin laminate where upon preparation the laminate will retain 90% of its pressed density, will not blister upon preparation and will not delaminate during the formation of the laminate.
This, and other objects of the present invention, are accomplished by means of the disclosure set forth herein below.